Is there a way to respond to text messages with voice to text?

Not directly, but can do it. After you receive a message, just invoke assistant and send a message to that person (as if it were a new message). Technically, it's not responding to the specific message but the result is the same, you send a message to that person.

thanks for the response.  The frustrating thing about that method is that my google assistant is terrible at recognizing my contact names so its not very helpful.  It would be better if I could just reply to the message like I do with Android Auto

Also, the watch wont give me a voice feedback even when I give it a command to text a contact.  It wont confirm who I'm texting or what my message is saying.  Is there a setting I am missing?  Is it not compatible with my phone?

I'd test it for you but I can't get Assistant to work from my watch. It's been unreliable. Garmin should either make it work consistently or remove the feature. As it is, seems it's not worth using. 

Its good to know that I'm not the only one.  I'm questioning why I paid an extra $150 over the vivoactive 5 which has all of the features except for the microphone and speaker.